High frequency circuits



April 17, 1934. J w LABUs 1,955,553

HIGH FREQUENCY CIRCUITS Filed Dec. 22, 1930 Inventor" John W. Labus,

by W

H is Attorney.

Patented Apr. 17, 1934 STATES HIGH FREQUENCY CIRCUITS John W. Labus, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application December 22, 1930, Serial No. 503,867

11 Claims.

My invention relates to high frequency circuits, such, for example, as those used for supplying high frequency oscillations to a radiating antenna, and it has for one of its objects to reduce the intensity of oscillations in said circuits having frequencies corresponding to undesired harmonics of the oscillations to be radiated.

A further object of my invention is to provide means for use in connection with electron discharge devices connected in push-pull relation whereby oscillations of an undesired harmonic frequency supplied to the load circuit may be neutralized.

A further object of the invention is to provide means for preventing the occurrence of standing waves of undesired harmonic frequency upon the output circuit, particularly when said output circuit comprises a transmission line of considerable length such that undesired radiation results therefrom.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing in which the single figure represents an embodiment of my invention.

Referring to the drawing, I have shown a pair of electron discharge devices 1 and 2 connected in push-pull relation to amplify oscillations supplied from a source of radio frequency oscillations 3 and to supply the amplified oscillations through an output transformer 4 to a transmission line 5 whereby they are supplied to a suitable load which I have indicated in the drawing as an antenna 6.

It frequently occurs in arrangements of the type indicated, where a transmission line 5 of considerable length is employed to transmit oscillations of desired frequency from a source to a remotely located radiating system, that conthe desired oscillations occur from the transmission line. These harmonics may be supplied to the line through extraneous capacities existing between the components of the circuits of the transmitting source and the line, and appear thereon as electromotive force between the line and ground; that is, the two opposite conductors of the transmission line oscillate in phase with respect to ground and therefore cooperate to produce radiation into space.

siderable radiation of harmonic frequencies of Thus, for example, in the arrangement shown in the drawing, in which the transmitting source includes electron discharge devices 1 and 2 con nected in the well known push-pull circuit arrangement, the grids of the tubes are excited in opposite phase relation from the source 3. By means of a source of potential 7 the grids are biased negatively to an extent sufficient substantially to preclude the flow of anode current when no oscillations are supplied from the source 3. When the grids are excited from the source 3 a current impulse flows in the output circuit of each device during the positive half cycle of the grid potential, these alternate impulses, of course, exciting the tuned circuit comprising the pri mary winding of transformer 4 and condenser 13 into oscillations, which are transferred to the transmission line 5 and radiated by the antenna 6. These alternate current impulses from both discharge devices, however, flow in the common portion of the output circuit, and accordingly, cause a voltage to appear across any impedance which exists in this common portion of the anode circuit having a frequency corresponding to the' second and higher even harmonics of the oscillations amplified by the discharge devices 1 and 2. This impedance may, for example, comprise the impedance of the source of potential '7 which is utilized to energize the anodes of the discharge devices, that of its icy-passing condenser 11, or any other impedance which may be connected in this common portion of the anode circuits. Accordingly, it will be apparent that the entire primary winding of the output transformer will oscillate with respect to the cathodes of the discharge devices at the second harmonic frequency of the oscillations amplified, and also at each of the higher even harmonic frequencies. Due to the capacity effect existing between the primary and secondary windings, this harmonic electromotive force is supplied to the secondary winding and to the transmission line conductors, thereby causing these conductors to oscillate in phase with respect to ground potential.

To neutralize these harmonic oscillations which arepsupplied through the transformer 4 to the transmission line, I have provided an inductance Shaving an intermediate point thereof connected to the cathode of the discharge devices 1 and 2 through the source of potential 7, and opposite points thereof connected to an intermediate point respectively on the primary and secondary windings. In this way currents of the harmonic frequency which flow through the right hand portion of the inductance 8 cause an electromotive force to appear between the intermediate point on the inductance 8 and the left hand terminal, this electromotive force being supplied to the secondary winding of the transformer in opposed phase relation to that which is impressed on the primary winding of the transformer due to the impedance of the common portion of the anode circuits. The connection to the secondary winding is made through a variable condenser 9 by means of which the magnitude of the charge supplied to the secondary winding through the condenser may be varied, so that this charge just neutralizes the charge which is supplied through the inherent capacitance of the transformer. In this way I have found that a very material reduction in radiation from a transmission line may be obtained.

Fiuther reduction in this radiation, however, may be obtained by connecting an impedance 10 between the transmission line and ground, this connection being made preferably at the end remote from the transmitter. As shown in the drawing this connection is made to a point between two equal condensers 12 which are provided in series across the remote end of the transmission line. These condensers are so adjusted as to terminate the transmission line in an impedance equal to the surge impedance of the line. The impedance 10, which may comprise a resistance, is equal to the surge impedance of the path in which the harmonic oscillations flow, this path comprising the two conductors of the transmission line considered as connected in parallel and the ground as the return path. Thus this impedance prevents any reflected, or standing, waves of the undesired harmonic frequency from occurring on the transmission line.

While I have shown particular embodiments of my invention, it will of course be understood that I do not wish to be limited thereto since different modifications thereof may be made, and that I contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. The combination, in a radio transmitter, of an antenna system, a source of radio frequency oscillations, a transmission line comprising a pair of conductors extending from said source to said antenna system, a coupling between said source and said transmission line being so arranged that oscillations of desired frequency are impressed between the conductors of said line and oscillations having the frequency of an undesired harmonic of said desired frequency are impressed between the conductors of said line and ground, and an impedance connected between ground and that end of said transmission line which is nearer the antenna system having a value equal to the surge impedance of the path in which said undesired harmonic flows whereby standing waves of said undesired harmonic frequency are prevented upon said line.

2. In combination, a pair of electron discharge devices, means connecting said discharge devices in push pull relation, a load circuit, means coupling said load circuit to the output circuits of said discharge devices, whereby desired oscillations appearing in the output circuit of said discharge devices and an undesired harmonic thereof are supplied to said load circuit, and means for supplying electromotive force with respect to the cathodes of said discharge devices to said load circuit, having a frequency corresponding to said undesired harmonic of said desired oscillations, said electromotive force being supplied in opposite phase to electromotive force of said undesired harmonic frequency supplied to said load circuit through said coupling means.

3. In combination, a pair of electron discharge devices, means connecting said discharge devices in push pull relation, a transmission line, means coupling said transmission line to the output circuits of said discharge devices, whereby desired oscillations appearing in the output circuit of said discharge devices and an undesired harmonic thereof are supplied to said transmission line, and means for supplying electromotive force with respect to the cathodes of said discharge devices to said transmission line, having a frequency corresponding to said undesired harmonic of said desired oscillations, said electromotive force being supplied in opposite phase to electromotive force of said undesired harmonic frequency supplied to said transmission line through said coupling means, and an impedance connected between ground and the end of said transmission line remote from said discharge devices, said impedance being equal to the surge impedance of the path including said transmission line in which cur rents of said undesired harmonic frequency flow.

a, in combination, a pair of electron discharge eices, means connecting said discharge devices transformer having primary and secondary windings, said primary winding being connected between the anodes of said discharge devices and having an intermediate point connected through an impedance to said cathodes, whereby increases in anode current occurring alternately at desired frequency in said discharge devices produce alternating electromotive force having said esired frequency between the terminals of said secondary winding and the potential of said primary winding with respect to said cathode oscillates at a frequency corresponding to an even harmonic of said desired frequency, and means for supplying an electromotive force between said cathodes and said secondary winding having said even harmonic frequency and in such phase and magnitude as to neutralize the electromotive force of said even harmonic frequency supplied to said secondary through the inherent capacity between said windings.

5. In combination, a pair of electron discharge devices, means connecting said discharge devices in push pull relation, said means including an anode circuit for each discharge device, said anode circuits having a common portion and individual portions, a load circuit, means coupling said load circuit to said individual portions, and means for deriving an electromotive force from the common portion of said anode circuits having a frequency corresponding to an undesired harmonic of the frequency at which said discharge devices operate and for supplying said electromotive force to said load circuit in opposed phase relation to electromotive force of said undesired harmonic frequency which is supplied to said load circuit through said coupling means.

6. In combination, a pair of electron discharge devices, means connecting said discharge devices in push pull relation, said means including a transformer having primary and secondary windings, said primary windings being connected between said anodes, and an inductance having an intermediate point connected to said cathode and opposite points thereon connected respectively to push pull relation, said means comprising a the midpoint of said primary Winding and to said secondary winding.

7. In combination, a source of high frequency oscillations, a radiating antenna, a transmission line arranged to transmit from said source to said antenna oscillations of a certain fundamental frequency, means for coupling said transmission line with said source, said coupling means being so constructed and arranged that oscillations having frequencies corresponding to harmonics of said fundamental are impressed upon opposite conductors of said transmission line in phase, and means to neutralize oscillations of said harmonic frequencies on said transmission line while maintaining the transmission of said fundamental frequency to said antenna.

8. The method of reducing undesired harmonic radiation from a transmission line, which is so coupled to a source of oscillations to be transmitted that said oscillations are impressed between opposite sides of said transmission line, and oscillations having a frequency which is a harmonic of the frequency of said oscillations to be transmitted are supplied to both sides of said transmission line in phase, which includes the step of supplying oscillations having said harmonic frequency to both sides of said transmission line in phase and in opposed phase relation to said first mentioned oscillations of harmonic frequency thereby to neutralize said harmonic oscillations on said transmission line.

9. In combination, a source of oscillations, a transmission line, means to impress oscillations of the frequency to be transmitted over said line to opposite sides thereof in opposite phase whereby currents of said frequency fiow in opposite directions in said opposite sides of said line, said means operating to impress oscillations having a harmonic frequency of the frequency to be transmitted over said line to the opposite sides thereof in like phase, and means to neutralize said harmonic frequency oscillations while maintaining the transmission of said fundamental frequency over said line.

10. In combination, an electron discharge device having an anode circuit, a transmission line, means for coupling said transmission line with said anode circuit, said coupling means being so constructed and arranged that oscillations of a fundamental frequency are supplied to opposite sides of said transmission line in opposite phase and oscillations having an undesired harmonic frequency are supplied to said opposite sides of said transmission line in like phase, means connected in said anode circuit to produce an electromotive force having said undesired harmonic frequency and opposed phase relation to the undesired harmonic frequency oscillations supplied to said transmission line, and means to supply said last mentioned oscillations to both sides of said transmission line in like phase thereby to neutralize said harmonic oscillations.

11. In combination, a high frequency transmitter having an output circuit, a transmission line, means to couple said output circuit to said transmission line to supply between opposite sides of said line oscillations of a desired fundamental frequency to be transmitted, said means operating to impress on both sides of said line in like phase oscillations having an undesired harmonic frequency of said fundamental frequency, and means connected between said output circuit and said transmission line to supply to said line 0scillations of said undesired harmonic frequency in opposed phase relation with respect to said harmonic oscillations supplied thereto by said coupling means.

JOHN W. LABUS. 

